Golang: map with multiple values per key

Question


 func ParseportsFromFile(file string) (map[string]string, error) {
            buf, err := ioutil.ReadFile(file)
            if err != nil {
                return nil, err
            }
            ret := [make(map[string]string)]
            rows := strings.Split(string(buf), "\n")
            for _, row := range rows {
                kvs := strings.SplitN(row, "=", 2)
                if len(kvs) == 2 {
                    ret[strings.TrimSpace(kvs[0])] = strings.TrimSpace(kvs[1])
                }
            }
            return ret, nil
        }

This function allows me to read a file like that :

user1=123 
user1=321 
user2=124

However, the data return is

map[user1:321 user2:124]

So that mean user1=123 has been overwritten with user1=321 How to avoid that ? How to create an array like map[user1:[123,321], user2: 124] to avoid an item to overwrite another ?

The Fool · Accepted Answer · 2022-05-15 11:36:20Z

5

Since go is strongly typed, it would be easier to make it right away a map of slices. See the http.Header type, for example. They had the same problem to solve when designing it.

In your case, this could look something like this:

result := make(map[string][]string)

for _, row := range rows {
    parts := strings.Split(row, "=")
    key := parts[0]
    value := parts[1]
    result[key] = append(result[key], value)
}

https://go.dev/play/p/5uRH-aQmATR

Otherwise, you need to use interface{} (any) so you can have both, string and []string, but the logic to get that done would be more complex, and using it would be also more complex since you always need to check what it is and do type assertion and so on. After all, I would not recommend it.

edited May 15, 2022 at 11:36

answered May 15, 2022 at 11:13

The Fool

21.2k7 gold badges76 silver badges123 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Golang: map with multiple values per key

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related